The present invention relates to magnetic heads and particularly to a magnetic write/read head for a recording medium wherein the recording medium is provided with at least one magnetizable storage layer which contains a magnetically anisotropic material, of which the axis of easy magnetization is aligned substantially perpendicularly to the surface of the medium and into which information can be written along a track by perpendicular magnetization of the storage layer. Such magnetic heads have a magnetic conductor body for carrying the magnetic flux having two pole legs which are arranged adjacent the other (one behind the other) in the direction of relative motion of the head and medium and have a predetermined distance from each other. At least one coil winding is associated with the pole legs, whereby, for performing the read function, the flux conduction directions in the two pole legs are arranged at least largely anti-parallel at the ends of the pole legs facing the recording medium. Such a magnetic head is known from DE-OS No. 29 24 013, corresponding to U.S. Pat. No. 4,287,544.
The principle of perpendicular magnetization for the storage of information is generally known, see, for instance, "IEEE Transactions of Magnetics," vol. MAG-16, no. 1, January 1980, pages 71 to 76 or the above-mentioned DE-OS No. 29 24 013. In order to employ this principle, which is often also called vertical magnetization, special recording media, for instance, in the form of a rigid magnetic storage disc, a flexible individual disc (floppy disc) or magnetic tape are required. Such recording medium has at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, particularly of a CoCr alloy of which the axis of easy magnetization is aligned perpendicularly to the surface of the medium. By means of a separate write head the individual bits of information are then written along a track in successive sections, also called cells or blocks, by magnetization of the storage layer. In practice, the magnetic flux changes, i.e., the transitions from one direction of magnetization to the opposite one, are generally used to record bits of information. The sections have a predetermined dimension in the longitudinal direction of the track which is also called a wavelength. This dimension can be substantially smaller than the limits given by the method of longitudinal storage by demagnetization, so that the information density in the recording medium can be increased advantageously by the principle of vertical magnetization.
With the principle of vertical magnetization, problems arise, however, in the development of corresponding combined write/read heads. In particular, difficulties arise with these heads due to the desired flux conduction in a circuit closed as far as possible having low magnetic resistance.
A suitable combined write/read head, i.e., a magnetic head with which the write as well as also the read function can be performed, comprises, in general, a so-called main pole, by which a sufficiently strong vertical magnetic field is generated for remagnetizing the individual sections in the storage layer. The necessary return for the flux can then take place, for instance, by a so-called auxiliary pole on the opposite side of the recording medium. See the mentioned literature reference "IEEE Trans. Magn.," vol. MAG-16. In addition, a return by leakage flux is also known. See "IEEE Trans. Magn.," vol. MAG-18, no. 6, Nov. 1982, pages 1170 to 1172.
A return can also be realized with a separate auxiliary pole which is located on the same side as the main pole. See "IEEE Trans. Magn.," vol. MAG-17, no. 6, Nov. 1981, pages 3120 to 3122 or vol. MAG-18, no. 6, Nov. 1982, pages 1158 to 1163, or German DE-OS No. 29 24 013 mentioned above. Accordingly, the magnetic write and read head known from DE-OS No. 29 24 013 contains on its foreward end face, as seen in the direction of motion of the recording medium moving below it, an auxiliary pole and on its back side the main pole proper. This main pole is formed by a pole leg which comprises essentially a thin pole piece which extends perpendicularly to the direction of motion and is applied to a nonmagnetic substrate. The auxiliary pole, which has a larger dimension as seen in the direction of motion and is disposed in front of the main pole, is formed by a pole leg which is composed of several thin pole pieces arranged perpendicularly to the direction of motion, with interposed insulating layers, and which is separated from the main pole via an air gap. The extent of this air gap is relatively large and is, for instance, on the order of 5 to 10 .mu.m. In the air gap is arranged an electrical winding by which the main pole can be excited for the write function and the excitation of the main pole can be registered for the read function. The auxiliary pole serves in any case only for returning the flux. Possible concurrent writing of the auxiliary pole can be tolerated because it is always followed by the writing main pole and information that might have been written by the auxiliary pole is written over unless the width of the auxiliary pole is larger than that of the main pole, and thus already written adjacent tracks remain uninfluenced. In addition, the larger cross section of the auxiliary pole as compared to the main pole and the relatively large extent of the air gap are also necessary in order to assure a sufficient reduction of the magnetic flux density at the auxiliary pole. Concurrent reading of the auxiliary pole can, however, lead to difficulties in information detection.
The remaining space of the air gap which is facing the recording medium and is not filled by the electric winding must be filled by a so-called insulating gap layer. This gap layer should comprise a material as hard as possible such as Al.sub.2 O.sub.3 in order to prevent notches or washouts during the manufacture of the head, since such unevennesses can lead to a crash, with the recording medium, of the magnetic head, which is guided at an extremely small distance, due to deposited dirt particles. It has been found, however, that the manufacture of this gap layer disposed between the main pole and the auxiliary pole is extremely difficult.
Due to the mentioned difficulties in reading with the known combined write-and-read head, the functions of writing and reading also can be carried out with separate heads, so that these heads can be optimally adapted to the respective functions. See, for instance, "IEEE Trans. Magn.," vol, MAG-16, no. 5, Sept. 1980, pages 967 to 972. For reading, known toroidal heads can be used, while writing must be carried out with special heads. A write head suitable for this purpose has, for instance, on its side facing the storage layer of the recording medium, a main pole, also designated as a single- pole head with a longitudinal dimension of, for instance, 3 .mu.m, opposite to which is disposed a substantially larger auxiliary pole on the backside of the recording medium. The second head, required only for reading, is a known toroidal head and has a gap width of, for instance, 0.2 .mu.m. See "IEEE Trans. Magn.," vol. MAG-17, no. 6, Nov. 1981, pages 2538 to 2540. Corresponding devices for reading and writing with heads specially adapted to the respective functions are relatively expensive to design.